This paper indicated a simulation study to optimizing the p-i-n InGaN homojunction solar cells. From the simulation results, it was found that optimized value of cell thickness is 1.3 μm and a maximum energy conversion about 20 % can be achieved in 1015 cm−3 defect concentration. It is shown that i-layer quality is a dominant factor in determining the performance of the cell. This result is consistent with the fact that InGaN p-i-n homojunction solar cell with higher densities of defects and dislocations exhibits a lower J sc and V oc, and consequently lower efficiency of the cell. Simulation results demonstrated that high-quality InGaN alloy is necessary to fabricate a high performance cell.